1. Technical Field
The present invention relates to a hybrid power driving system of a vehicle, in particularly, to a hybrid power driving system including a planetary coupling mechanism and a speed-reduction mechanism, moreover, to a gear position operation method thereof.
2. Description of the Related Art
The requirements on motor vehicle emissions have become increasingly strict. The performance of pure electric vehicles (EV) may not meet the power requirements under certain conditions. Hybrid power vehicles (HEV) have developed quickly because of their advantages in power performance and environment protection.
A hybrid power vehicle has two different power sources: an electric motor and an internal-combustion engine. A hybrid power driving system can be classified in different types: a serial drive system, a parallel drive system and a series-parallel power drive system. In a serial drive system, an internal-combustion engine drives an electric generator to generate electricity which is used to drive an electric motor. The electric motor in turn provides power to the vehicle. In a parallel drive system, an internal-combustion engine and an electric motor together drive the vehicle. The engine and motor belong to two systems, and may separately provide torques to a transmission system of the vehicle and may separately or together drive the vehicle under different road conditions. In a series-parallel power drive system, the power of an internal-combustion engine and the power of an electric motor are combined and then sent to a transmission system of the vehicle. Due to developments in power coupling technology and electric motor-generator conversion technology, there are more and more types of series-parallel power drive systems.
The electric motor-generator conversion technology is quite mature at this time. Its main principle is that by adding a circuit conversion component, an electric motor may be used not only as a motor but also as a generator. For example, for a direct current motor, the working principle of a direct current motor and that of a permanent magnet generator are all based on the electromagnetic induction principle. The difference is just that, for the direct current motor, the motor rotor is subject to a force in a magnetic field when an electric current passes through the motor rotor; for the permanent magnet generator, the rotor of the generator is rotated to cut through magnetic field lines to produce a current. Thus, adding circuit conversion components and the brushes of a direct current motor to a permanent magnet generator allows an electric motor to selectively operate as a generator or a motor. This device is called a motor-generator unit, in short a “motor-generator.”
Moreover, one of the important technologies concerning the series-parallel driving system is the power coupling technology for the internal-combustion engine and the electric motor. For example, Chinese patent CN2693516Y discloses a hybrid power driving system for a vehicle. As shown in FIG. 3, the driving system includes an internal-combustion engine 100, an electric motor 200 and a planetary gear mechanism used as the power coupling mechanism. The planetary gear mechanism includes a ring gear 400, a planet carrier 500 and a sun gear 600. The electric motor 200 transmits power to the ring gear 400 via a gear designated by reference numeral 300, and the internal-combustion engine 100 transmits power to the sun gear 600. Then the powers from the electric motor 200 and the internal combustion engine 100 are combined via the planet carrier 500 and transmitted to the driving system of the vehicle.
As is known, the rotational speed of the internal-combustion engine or motor is quite high. Before the rotation of the internal-combustion engine or motor is transmitted to a driving wheel of the vehicle, the speed is reduced and the torque is increased by a speed-reduction mechanism. This is true for a hybrid power vehicle. This speed-reduction mechanism is mainly composed of a speed-reduction gear system. The reduction ratio is fixed after the manufacture of the speed-reduction gear system. In order to satisfy the need of speed reduction and torque increase for the vehicle under different operating conditions, a traditional drive system, driven by only an internal-combustion engine, has a transmission for different gear positions. However, for a hybrid power drive vehicle, due to the arrangement of the power units (the internal-combustion engine and electric motor) and the limitations imposed by the power coupling mechanism, the use of a transmission not only complicates the structure of the driving system but also makes it more difficult to assemble. Therefore, the reverse gear for the hybrid power vehicle is mainly realized by controlling the forward and reverse rotation of the electric motor, and the speed of the vehicle is varied mainly by adjusting the rotational speed of the motor in a way similar to that of a continuously variable transmission. Accordingly, the output rotational speed of the electric motor is varied by changing the output power of the electric motor.
However, this method for varying speed cannot satisfy a vehicle's need under different operating conditions. For example, for the hybrid power driving system disclosed in the aforementioned patent CN2693516Y, when the vehicle is climbing a slope (assuming that the gradient of the slope is the maximum gradient that the vehicle with a full load can climb), the combined output power of the internal-combustion engine 100 and electric motor 200 needs to be at the maximum value. This requires the output rotational speed of the electric motor 200 to be at the maximum value. But the output rotational speed of the electric motor 200 must be reduced by a speed-reduction mechanism to increase the torque to drive the vehicle to climb the slope (especially when the vehicle with a full load has a large mass). To satisfy this operating condition, the reduction ratio of the speed-reduction mechanism must be quite large. However, a large reduction ratio for the speed-reduction mechanism of the hybrid power driving system does not meet the needs of the vehicle in other operating conditions. For example, when the vehicle travels at a high speed on a flat road with no load, even if the rotational speed of the combination of the motor 200 and internal-combustion engine 100 is at the maximum value, the vehicle speed may still be too low because of the large speed reduction ratio of the speed-reduction mechanism.
From the aforementioned, the conventional method for varying the speed of a hybrid power vehicle does not satisfy the need of a vehicle under different operating conditions. This has always been a difficult problem in the design of a hybrid power vehicle.